What to watch out for and what you need to know as Americans cast their vote

Armchair election watchers brace yourselves; it’s going to be a marathon.

Here is a guide outlining the principle elements to look out for as President Barack Obama and challenger Mitt Romney go toe to toe.

POLLS OPEN: The continental US covers four times zones. Aside from Dixville Notch, the New Hampshire village whose 12 residents vote just after midnight tonight, the earliest polling stations open at 11:00 GMT in Virginia and New Hampshire, among other eastern states. On the west coast, California polls open at 15:00 GMT.